1. Field of the Invention
The present invention relates generally to an apparatus for manufacturing a semiconductor device and, more particularly, to a dry etching apparatus capable of monitoring the motion of the wafer area pressure (WAP) ring and the plunger shafts that actuate the WAP ring.
2. Description of the Prior Art
Plasma etching has become the preferred technique for etching patterns in the various layers utilized in the manufacture of integrated circuit devices. The apparatus for such etching typically includes a chamber housing a pair of essentially planar electrodes that are spaced apart in a parallel relationship to define an interaction space therebetween. On a lower electrode is positioned a semiconductor wafer being processed. For such processing, an appropriate gaseous medium is introduced into the chamber and then one or more suitable high radio-frequency voltages are impressed across the pair of electrodes to generate discharge and form plasma that etches suitably exposed regions of the wafer.
It has become of increasing importance both for efficiency and for uniformity to confine the plasma essentially to the interaction space between the two electrodes. To this end, it has been proposed to include a ring-shaped element (a plasma confinement ring) at the periphery of one or both of the electrodes to confine the discharge to the interaction space. Such plasma confinement ring is also known as a wafer area pressure (WAP) ring, which is provided to confine the plasma stream to the area of the wafer.
FIG. 1 is a schematic, cross-sectional diagram illustrating the arrangement of a top electrode and WAP ring of a conventional plasma etching apparatus. As shown in FIG. 1, the plasma etching apparatus 10 comprises a lower assembly 12 and an upper portion 13. The lower assembly 12 generally includes a disk-shaped electrostatic chuck (ESC) 12a, a focus ring 12b, and a ground ring 12c. The ESC 12a is capable of holding a wafer 20 and is typically serves as a bottom electrode or anode. The focus ring 12b extends around a peripheral portion of the ESC 12a. The upper portion 13 generally includes a top electrode or cathode 14 and a WAP ring 16. The WAP ring 16 encircles the top electrode 14. Typically, the WAP ring 16 includes a thicker twist ring 16a and three thinner lower rings 16b, 16c and 16d. Both the lower assembly 12 and the upper portion 13 are installed in a chamber housing 25.
Generally, the WAP ring 16 is connected to three plunger shafts 32 (only one of the three shafts is shown). One end of each of the three plunger shafts 32 is further connected with a movable lower roller 34. The lower roller 34 is bonded to a corresponding fixed upper roller 36 with a resilient means such as spring (not shown). An annular cam 40 reciprocally moves along the direction 42 between the lower roller 34 and the upper roller 36 such that the WAP ring 16 descends and ascends between the “home position” as shown in FIG. 1 and the “work position” as shown in FIG. 2.
One drawback of the above-described prior art is that a gap 18 between the top electrode 14 and the WAP ring 16 is very small, which is typically about 0.02 inch or less. During the descending and ascending of the WAP ring 16, even very small discrepancy between the three plunger shafts 32 results in oblique WAP ring and undesired rubbing or scratching of the top electrode 14 and the WAP ring 16, thus causing particle contamination of the chamber or wafer. The discrepancy between the three plunger shafts 32 may result from fatigue of the spring or worn rollers or parts.
It is desirable to precisely control the descending and ascending of the WAP ring 16 in a horizontal manner and to provide a system to monitor the abnormal motion of each of the three plunger shafts 32 during descending and ascending of the WAP ring 16, thereby preventing particle contamination of the chamber or wafer.